1 in 11 babies born in America this year will be screened by a genetic test that didn't exist a decade ago. Biotech startup @BillionToOneInc turned a simple but radical idea—detecting rare fragments of fetal DNA in a mother's blood—into one of the most widely used prenatal tests in the U.S. And they're not stopping there. The same approach could unlock something even bigger: early-stage cancer detection from a blood test, a breakthrough that could one day save millions of lives. In this…